In brief: the IPCC Climate Change 2014 Synthesis Report

Ignorance can no longer be used as an excuse for no action Michel Jarraud – World Meteorological Organization

What is the Synthesis Report?

The newly published IPCC Synthesis Report, released on 2nd November, draws together the key findings of the three Working Groups of the IPCC (The Physical Science Basis; Impacts, Adaptation, and Vulnerability; Mitigation of Climate Change – available here) as well as two Special Reports. It forms the final, and possibly most important, instalment of the IPCC’s Fifth Assessment Report (AR5).

The Synthesis Report will provide the new road map for politicians and policy makers, and has already received widespread support by world leaders. It is especially significant given that the United Nations Climate Change Conference is scheduled for 2015 in Paris.

“The scientific case for prioritising action on climate change is clearer than ever… Beyond a certain point, human society cannot cope with the change, and therefore, the IPCC has drawn up a very clear rationale for the society to deal with this problem,”

Dr Rajendra Pachauri, IPCC Chairman

What are the key messages?

The Synthesis Report is divided into four topics. Here, we distil the key messages from each section.

1: Observed changes and their causes

The report indicates that human influence on the climate system is clear, and there is now unequivocal evidence for climate warming.

Total anthropogenic greenhouse gas emissions continued to increase from 1970 to 2010, with larger absolute increases between 2000 and 2010. This is despite the increasingly widespread adoption of climate change mitigation policies. In 2010, anthropogenic greenhouse gas emissions reached 49 ± 4.5 GtCO2 eq/yr; the highest ever recorded. In fact, atmospheric concentrations of carbon dioxide, methane, and nitrous oxide now far surpass greenhouse gas levels recorded in the ice cores over the last 800,000 years.

Since the 1950s, many of the observed changes are unprecedented; “the atmosphere and ocean have warmed, the amounts of snow and ice have diminished, and sea level has risen” and “each of the last three decades has been successively warmer at the Earth’s surface”.

Ocean warming accounts for over 90% of the energy accumulated on Earth between 1971 and 2010. Only around 1% is stored in the atmosphere. Globally, ocean warming has been greatest near the surface – the upper 75 m have warmed 0.11°C per decade from 1971 to 2010.

Since the beginning of industrialisation, oceanic uptake of CO2 has resulted in ocean acidification. Ocean surface pH has decreased by 0.1. This is the equivalent of a 26% increase in ocean acidity.

From 1901 to 2010, global mean sea level rose by around 0.19 m, and the rate of sea level rise since the mid 19th century has been much greater than that of the previous two millennia.

Changes in extreme weather and climate events have been observed since the 1950s.

2: Future climate change, risks and impacts

Surface temperature is projected to rise over the 21st century under all four assessed emission scenarios:

RCP 2.6, when emissions peak between 2010 and 2020

RCP 4.5, when emissions peak around 2040

RCP 6.0, when emissions peak around 2080

RCP 8.5, when emissions continue to rise throughout the 21st century

For many regions, it is very likely that heat waves will be more frequent and long-lived; and extreme precipitation events will become more frequent and intense. There will continue to be occasional cold winter extremes.

There have been major improvements in scientific understanding, and prediction of, sea level change since the publication of the previous IPCC report (AR4).

The ocean will continue to warm and acidify, and global mean sea level will continue to rise – very likely at a faster rate than that observed from 1971 to 2010.

Arctic sea ice will reduce, year round, under all four assessed emission scenarios.

It is almost certain that near-surface permafrost will decrease in extent at northern high latitudes, under all four assessed emission scenarios.

The effects of climate change will continue for centuries, even if anthropogenic emissions are stopped. Warming will continue beyond 2100 under all emission scenarios except RCP 2.6. The risk of irreversible environmental change increases as the magnitude of warming increases.

Even if temperatures are stabilised, other parts of the earth system will not necessarily respond immediately. Biomes will continue to shift, soil carbon will alter, ice sheets will adapt their behaviour, and sea levels will adjust over their own long-term timescales, potentially lasting hundreds or thousands of years, after global surface temperature has stabilised.

Limiting climate change, its impacts, and its risks, requires a substantial and sustained reduction in greenhouse gas emissions, coupled with adaptation.

3: Future pathways for adaptation, mitigation and sustainable development

There are mitigation strategies that could limit warming to below 2°C relative to pre-industrial levels. However, these strategies would need significant cuts in emissions over the next few decades and near zero emissions of CO2 and other long-lived GHGs by the end of the 21st century

Mitigation and adaptation strategies need to be used together; they are complementary tools for tackling climate change over multiple spatial and temporal scales. These comprehensive reductions in emissions would bring with them significant economic, social, political, and technological challenges.

Mitigation in the near-term can help to reduce climate change impacts in the long-term, beyond the 21st Adaptation can help us to address both current and future risks.

The report identifies five “Reasons For Concern” (RFCs):

Unique and threatened systems

Extreme weather events

Distribution of impacts

Global aggregate impacts

Large-scale singular events

Adaptation planning and implementation is best achieved by operating at multiple scales, from individuals to governments and international panels.

4: Adaptation and mitigation

There are many adaptation and mitigation strategies available to us to help address climate change. But no single option will be effective by itself – we need to use multiple, complementary approaches.

Effective implementation of these approaches will depend on multiple scales of cooperation, linking mitigation and adaptation to wider social objectives.

We need to operate at all scales – international, regional, national, sub-national, and individual

Climate change is a threat to sustainable development, but there are ways that we can manage the potential impacts of climate change.

The cost of taking action to keep temperature rise under 2°C over the next 76 years will cost about 0.06% of GDP every year. Over the same period, world GDP is expected to grow at least 300%

IPCC

What are the implications of the report?

Overall, the latest report does not focus on new scientific findings but instead makes the IPCC’s previous conclusions even more clear, and difficult to ignore. The IPCC’s chairman, Dr Rajendra Pachauri, has said that the report was the “strongest, most robust and comprehensive” they have produced. Though the report is produced as an advisory document, it provides the strongest evidence of the causes and impacts of climate change, and highlights the necessity to adapt and mitigate against them.